Waveguide laser

ABSTRACT

A laser waveguide, where the laser waveguide can be formed by electrodes and at least one sidewall in a manner allowing a more compact structure than previously provided. Protrusions in the electrodes allow easier laser starts, and sectional sidewall(s) allow easier fabrication of sidewall(s), decreasing manufacturing costs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patentapplication No. 60/467,542 filed on 2 May 2003.

FIELD OF THE INVENTION

The invention relates in general to waveguide lasers and particularlybut not exclusively to RF excited waveguide lasers.

BACKGROUND OF THE INVENTION

A waveguide laser typically consists of two mirrors, concave or fiat,defining an optical resonator cavity coupled together with a waveguidedefining an optical path between the mirrors.

The waveguide is typically a channel ground into a ceramic block (e.g.aluminum. oxide, Al₂,O₃) with a lower electrode of aluminum or copperadded to complete a cross-section of the waveguide. Alternatively, thewaveguide can be ultrasonically drilled down through a piece of ceramicsuch as aluminum oxide (Al₂O₃) to create a continuous closed bore lengthwith upper and lower electrodes parallel to the bore length. Typically,the positive arm of the oscillating electromagnetic field (e.g. RadioFrequency—RF) supply will be coupled into the upper electrode of thewaveguide, and the ground plane of the RF supply will be coupled to thelower electrode. Resonance is added between and along the length of theupper electrode to distribute the RF voltage evenly along the length ofthe electrodes. Finally, the mirrors and waveguide structure are alignedand housed in a vacuum vessel (laser housing) that holds the gas to beexcited.

Waveguide lasers suffer from the disadvantage that, for the lengthsneeded, the waveguides are difficult to fabricate with sufficientaccuracy at a reasonable cost to obtain acceptable laser performance. Itis very difficult to cost-effectively fabricate a typical waveguidestructure that is roughly 30 to 40 cm long with a 1.5 to 3.0 mm bore.Bore cross-section inaccuracy leads to unacceptable laser transversemode characteristics and reduced power output. Due to the size, currentceramic slabs used to manufacture waveguides are constructed by castingor extruded. Casting or extruding tolerances are high, requiringexpensive machining (grinding) after the piece is formed to acquire thedesired accuracy.

Additionally, a waveguide laser balances it's loss in inherent internalRF circuit, and heat removal efficiency. Ideally, to minimize the RFlosses the capacitance between the top and bottom electrodes (RF+ andRF− or ground) needs to be high, which translates into using as littleceramic as possible between the top and bottom electrodes. With Al₂,O₃,thermal efficiency requirements dictate the use of a large ceramic area,which creates either a higher loss RF circuit, and/or high manufacturingcosts. Ideally materials with good thermal properties such as BeO andAIN are desirable ceramics to use, but are prohibitively expensive withrelated art waveguide designs.

Additionally, the resonator cavities of waveguide lasers suffer energylosses from misalignment of the containment mirrors and low reflectivityproperties of the containment. For example, the use of planar mirrors ateither end of the resonator cavity, unless perfectly aligned, enableonly a limited number of reflections.

Since the bore cross-sections, in the related art, are the result ofgrinding or ultrasonic drilling, most bores are either rectangular orcircular. This results in bores that are optimized for the manufacturingprocess rather than the optical properties of the device. For example,the use of curved containment mirrors results in variable beam radiusthroughout the resonator cavity, thus the waveguide channels of relatedart fail to allow the optimization of the waveguide with respect tovariable beam radius in the resonator channel.

In related art, the electrode positioning, and subsequent resonanceelectric field generation, is partly a function of the electrodespacing, and is often determined by the size of the waveguide structure(i.e. the distance between electrodes). Various spacing betweenelectrodes results in varying power levels and the related art fails tofully optimize the electrode spacing and optics, and insteadconventional methods focus on ease of manufacture.

Additional problems exist in conventional gaseous lasers, for example,laser startup. Traditional CO₂ lasers are pressurized at 70-80 torr andhave difficultly starting without some manipulation of the RF system.

A related art system is described in Laakmann (U.S. Pat. No. 4,169,251).Laakmann is directed to a conventional waveguide laser that suffers frommany of the same problems as other conventional systems (e.g., expensivelong ceramic pieces that must be formed via casting, conventionalstartup characteristics . . . ).

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention provide methods ofgaseous laser construction.

Exemplary embodiments of the present invention provide methods anddevices for the use of ceramic portions in the formation of laserwaveguides.

Exemplary embodiments of the present invention provide methods anddevices for the use of protrusions (e.g., electrode corner radii . . . )in the formation of laser waveguide structures.

Exemplary embodiments of the present invention provide methods anddevices for the combination of protrusions with the use of ceramicportions in the formation of laser waveguides.

Exemplary embodiments of the present invention provide for increasedlaser power and/or efficiency by optimizing electrode spacing.

An exemplary embodiment of the present invention provides a waveguidelaser having a waveguide located in a laser resonator cavity defined bya first and second reflecting means at opposite ends of the waveguideenclosed in a sealed vessel. The waveguide structure is made up ofmultiple pieces that when joined together form the waveguide walls. Thewaveguide walls can be made up of individual pieces that allow the wallsto be more accurately aligned. The individual pieces can be abutted oneto another, or can be separated by a gap with little degradation in thelaser power or mode.

Further areas of applicability of embodiments of the present inventionwill become apparent from the detailed description provided hereinafter.It should be understood that the detailed description and specificexamples, while indicating exemplary embodiments of the invention, areintended for purposes of illustration only and are not intended tolimited the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will become apparent from thefollowing detailed description, taken in conjunction with the drawingsin which:

FIG. 1 shows a perspective view of a slab waveguide laser according toan exemplary embodiment of the present invention;

FIG. 2 shows a cross-sectional view of a waveguide laser according to anexemplary embodiment of the present invention;

FIG. 3 shows a longitudinal view of section IV-IV of FIG. 4 of a laser,according to an exemplary embodiment of the present invention;

FIG. 4 shows an end view from the output coupler end of the laser,according to an exemplary embodiment of the present invention;

FIG. 5 shows an enlarged view of a waveguide section according to anexemplary embodiment of the present invention;

FIGS. 6A-6E show various laser waveguide cross sections in accordancewith exemplary embodiments of the present invention;

FIG. 7 shows a cross-section of a variable length-wise waveguide inaccordance with exemplary embodiments of the present invention;

FIG. 8 illustrates an exploded view of a waveguide with single piececeramic sidewall forming the walls of a waveguide structure inaccordance with an exemplary embodiments of the present invention;

FIGS. 9A-9C show various waveguide electrode protrusions in accordancewith exemplary embodiments of the present invention; and

FIG. 10 illustrates a power source connection in accordance withexemplary embodiments of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION

The following description of exemplary embodiment(s) is merelyillustrative in nature and is in no way intended to limit the invention,its application, or uses.

FIG. 1 shows a slab waveguide laser 1 according to an exemplaryembodiment of the present invention, comprising a top or upper electrode2 and a bottom or lower electrode 4. The upper and lower electrodes 2and 4 respectively, can have variable shape (e.g., planar, variablethickness, curved . . . ). Sidewalls 3 a, 3 b, 3 c, and 3 d aresandwiched between the upper electrode 2 and the lower electrode 4 andcan be separated by small gaps 5. The width and thickness of thesidewalls are shown shaded. The length of the sidewalls are not shaded.

The sidewalls 3 a, 3 b, 3 c, and 3 d and the upper and lower electrodes2 and 4 respectively can form a waveguide 6. There can be gaps 5 betweenthe sidewalls 3 a, 3 b, 3 c, and 3 d or no gap. In exemplary embodimentsof the present invention there can be any number of gaps. In additionalexemplary embodiments of the present invention, the sidewalls can sealthe waveguide 6 at a predetermined pressure. The waveguide 6 can besealed at various pressures depending upon the lasing medium or desiredoperating conditions. For example the waveguide can have electrodes 2and 4, sidewalls 3 a, 3 b, 3 c, and 3 d with no gaps. In this exemplaryembodiment the side walls 3 a, 3 b, 3 c, and 3 d extend and surround theelectrodes 2 and 4 to form the housing of the laser itself. Likewise theelectrodes 2 and 4 can form the housing of the laser (e.g., FIG. 6C).

The sidewalls 3 a, 3 b, 3 c and 3 d (etc) act to guide the beam to anextent that there is little or no appreciable beam degradation or powerloss even if there are gaps between the sections of the sidewalls orsections of the sidewalls and electrodes 2 and 4. Gaps 5 can be ofvariable size (e.g. 1-3 mm or more, . . . ) without affecting the beam.FIG. 2 shows an end-on view through a transverse section of thewaveguide laser 1 of FIG. 1. The upper electrode 2 and the lowerelectrode 4 are shown shaped so as to form the waveguide 6, with roundedcorners (protrusions). The shape of the electrodes 2 and 4 are easilychanged such that easier striking and better mode control of the beam isprovided. In waveguided lasers and other types of lasers, it is desiredfor circular symmetry to exist in the beam, which will produce thetypical Gaussian shape to the beam intensity. The electrodes may berounded further than is shown such that there is complete circularsymmetry in the waveguide, i.e. the waveguide is completely circular incross-section (e.g. as shown in waveguide 6 of FIG. 6A). In accordancewith exemplary embodiments of the present invention the variable shapingof the cross section of the electrodes can be shaped by conventionalmethods (e.g., by CNC Milling, . . . ).

FIG. 3 shows a longitudinal view of section IV-IV of FIG. 4 inaccordance with an exemplary embodiment of the present invention. Thelaser 1 can be disposed within a housing II and comprises a cavitycontained between the two ends 1 a and 1 b. End 1 a comprises areflective surface and end 1 b comprises a partially reflective surfacewhich forms the output coupler. The RF feed-through 12 can be encircledin an insulating ceramic casing 13. The ceramic casing 13 can becomprised of various materials (e.g., BeO, AIN, Al₂O₃, other suitableinsulating and/or dielectric material(s)). Although discussion hereinhas referred to various components, the arrangement of such componentsand the presence of such components should not be interpreted as beinglimitative on the scope of the present invention. For example, inaccordance with exemplary embodiments of the present invention, aseparate housing is not needed in a sealed waveguide structurecontaining reflective elements, where the sidewalls or electrodesadditionally form the housing.

The laser 1 can be contained in a housing 11, with an electrode top orupper plate 2 and bottom or lower electrode plate 4. The top or upperelectrode 2 is shown here as continuous but can also comprise one ormore sections to assist in alleviating warping due to temperaturedifferentials between the topside and bottomside of the electrodes. Thewaveguide 6 can be between a total reflector 14 and a partiallyreflecting surface 15. The total reflector 14 and partially reflectingsurface 15 can be placed at the waveguide's 6 ends. The partiallyreflecting surface 15 can form the output coupler for the beam. The beamcan make one or more passes through the waveguide before exiting at theoutput coupler. Exemplary embodiments of the present invention shouldnot be interpreted to be limited with regard to the number of waveguidesplaced between the total reflector 14 and the partially reflectivesurface 15. Exemplary embodiments of the present invention can havemultiple waveguides, where the waveguides can be connected or separate.

The exemplary embodiment of FIG. 3 illustrates a case where the ceramicsidewalls, 3 a, 3 b, 3 c, 3 d, 3 e are abutted to each other, leaving nogaps. In this embodiment of the invention, four ceramic cylinders 16 a,16 b, 16 c and 16 d are used to provide a clamping force between thelaser housing and the electrode assembly to hold the laser together. Thecylinders 16 a, 16 b, 16 c, 16 d can be made of various materials (e.g.,BeO, AIN or Al₂O₃, other suitable ceramic, . . . ). They are shown hereeach provided with an inductor 17 a, 17 b, 17 c, 17 d, which ensuresthat the voltage difference along the length of the laser is minimized.In exemplary embodiments, at least one power source can be connected viaconnector 12.

Screw adjustors 18 a and 18 b can be used to adjust the optics. Otheradjustors can be used to adjust the optics in other planes. Embodimentsof the present invention are not limited by the type of optical adjusterand other methods commonly known by one of ordinary skill can be used.The present invention is also not limited to having an optical adjustor.

FIG. 4 shows an end on view of a laser is accordance with an exemplaryembodiment of the present invention. Two optic adjustments means 18 canbe placed orthogonal to each other to facilitate the adjustment of theoptics in two planes, both perpendicular to the optical axis of thebeam, the optical axis lying parallel to the bore 6. Other adjustmentmeans, not shown, can be used for adjustment of the optics in thedirection parallel to the beam.

FIG. 5 shows an enlarged view of the electrodes and waveguide of FIG. 2in accordance with an exemplary embodiment of the present invention,showing more clearly the electrodes 2 and 4. The electrodes 2 and 4 areprofiled to provide a shaped waveguide 6. The electrodes 2 and 4 can beformed with any desired shape to optimize power and beam quality. Theprofile portion of the electrodes is herein also referred to as aprotrusion(s).

FIGS. 6A-6E show various cross sections of waveguides 6 in accordancewith exemplary embodiments of the present invention. In FIGS. 6A through6D, the waveguides 6 are surrounded by electrodes 2 and 4 and sidewallpieces 9A and 9B. The electrodes 2 and 4 and the sidewall(s) can havegaps and not lie flush upon each other. FIG. 6C shows the use of anelectrode 2 to form a majority of the housing of a laser waveguide inaccordance with an exemplary embodiment of the present invention.Electrode 2 is separated from electrode 4 by an insulative spacer 10,which can be a protruded part of the ceramic side walls 9A and 9B. Infurther exemplary embodiments of the present invention the sidewall(s)can form the housing.

Multiple waveguides (6A, 6B, and 6C) are shown in the exemplaryembodiment of the present invention shown in FIG. 6E. As illustrated inFIGS. 6A-6E, exemplary embodiments of the present invention can havemultiple shapes of the waveguide 6, multiple shapes and numbers of theelectrodes 2 and 4 (e.g. 2A, 2B, 2C, 4A, 4B, and 4C), multiple numbersof waveguides (e.g., 6A, 6B, and 6C), and multiple numbers of side wallpieces (e.g. 9A, 9B, 9C and 9D). Additionally, the waveguides can beconnected at a location along their lengths. Likewise exemplaryembodiments of the present invention can have insulators 10, 10A, 10B,10C, and 10D to insulate the electrodes from each other. In an exemplaryembodiment of the present invention one of the multiple waveguides shownin FIG. 6E has no electrodes activated and the chamber acts as a coolingchamber for lasing gas. Where the cooling chamber is one of thewaveguides connected to second waveguide somewhere along the length ofthe waveguide. Where the second waveguide has active electrodes andlasing occurs.

FIG. 7 shows a two dimensional lengthwise cross-section of a laserwaveguide in accordance with an exemplary embodiment of the presentinvention. The waveguide 6 has a variable cross-section, in thelengthwise direction, designed specifically for maximizing opticalefficiency. The variable cross-section can be of varying shape dependingon the optical modes in the waveguide 6. Although FIG. 7 illustrates asymmetric variable shaped cross-section in the lengthwise direction, theshape can be asymmetric or non-symmetrical.

Additionally the side walls forming the waveguide 6 can be connected bya strip essentially forming one sidewall with two separate sides. If onesidewall is formed then the strip adjoining the two separate sides cancover the surface of one electrode at a position along the length of thewaveguide 6. FIG. 8 illustrates an exploded view of a laser waveguide inaccordance with an exemplary embodiment of the present invention havingone sidewall with two main sections 3A and 3B. The main sections 3A and3B can be connected by a strip 17, forming a single sidewall. The strip17 can also be used to place the electrodes 2 and 4, and there can bemany such strips of various shapes and sizes. The waveguide 6 is formedby two surfaces of the main sections 3A and 3B and surfaces of the twoelectrodes 2 and 4. The discussion herein should not be interpreted tolimit the scope of the present invention to sidewalls with a stripconnection or to one sidewall. Exemplary embodiments of the presentinvention can have multiple non-connected sidewalls.

Protrusions aid in the starting characteristics of a laser. FIGS. 9A-9Cshow some exemplary embodiments of the present invention wherein theelectrodes 2 and 4 contain protrusions 21. The protrusions 21 of theelectrodes 2 and 4 aid in the starting characteristics of a laser byincreasing the electric field in a localized region. For example a CO₂waveguide laser in accordance with an exemplary embodiment of thepresent invention, having protrusions, can start at 200 Torr pressure asopposed to 70 Torr. The starting pressures given by way of exampleshould not be interpreted to be limitative of the present invention.Lasers in accordance with exemplary embodiments of the present inventioncan start at various pressures.

In the exemplary embodiments of the present invention described above,the sidewalls (e.g., 3 a, 3 b, 3 c, 3 d, 9A, and 9B) can be constructedof various materials depending on the dielectric properties desired. Forexample the sidewalls can be constructed of ceramic materials (e.g.,Beryllium Oxide (BeO), Aluminium Nitride (AIN), . . . ) which are farsuperior in thermal and other characteristics to Aluminium Oxide(Al₂O₃), often used in related art waveguide lasers. BeO and AIN aresignificantly more thermally efficient and significantly more reflectivethan Al₂O₃. For example, BeO is approximately ten times more thermallyefficient. Exemplary embodiments of the present invention allowefficient use of the sidewalls such that the above mentioned materialscan be used. Exemplary embodiments of the present invention can also useAl₂O₃.

In the exemplary embodiments of the present invention the upper (e.g.,RF positive electrode) can be continuous to facilitate the distributionof the RF energy, or sectional. The sidewalls and the lower (e.g.,ground electrode) can be continuous and/or manufactured in individualsections and assembled. Individual sections aid in reducing overall costby providing a low cost standard repetitive platform that can beduplicated and aligned to produce a high quality waveguide structure.The sectional structure will result in reduced cost compared towaveguide structures presently in use. The discussion herein should notbe interpreted to limit the present invention to a particular sizesectional piece. Various sizes can be used for the length of thesectional pieces besides three inches (e.g., more than 80.0 mm, lessthan 80.0 mm) in accordance with exemplary embodiments of the presentinvention. For example in an eighteen inch laser, three sectional piecescan be approximately six inches in length or in a six inch laser eachsectional piece can be two inches in length (if there are threesectional pieces. The discussion herein should not be interpreted tolimit the dimensions of the sectional pieces. Exemplary embodiments ofthe present invention additionally contain various sectional pieces,where the pieces are not of equal length and/or width and/or thickness.

Laser waveguides in accordance with exemplary embodiments of the presentinvention can have shorter side walls than related art waveguides. Ifthe side walls are formed of sectional pieces, such as less than threeinches, ceramics with favorable thermal properties (e.g., BeO, AIN, . .. ) can be used effectively and at a lower cost. Ceramics with favorablethermal reflectivity properties can maintain a high thermal conductivitywhile minimizing RF circuit losses.

The pieces can be formed by pressing, sintering or casting. Pressingallows the use of less milling (light milling) to obtain the tolerancesneeded, thus there is less milling costs. Milling of ceramic is oftenreferred to as grinding. Sintering and casting are relatively cheap. Forexample, although BeO is approximately twice the price of Al₂O₃ yet itis approximately ten times more thermally conductive than Al₂O₃. AIN isapproximately five time more thermally conductive. Since conductively isgreater, less material is needed, and the resulting cost is reduced. Inaddition to cost savings, the superior reflectivity available from thesematerials provides higher efficiency.

In an exemplary embodiment of the present invention a gaseous lasingmaterial is used such as CO₂ or mixtures thereof (e.g. CO₂, He, N₂, . .. ). A CO₂ waveguide is unlike a fiber optic waveguide in severalrelevant respects. The CO₂ waveguide is referred to as a “leaky mode”waveguide, so gaps in the waveguide are possible and cause little or noadverse changes to the optical properties. Thus, the multiple pieces ofceramic or other suitable material (e.g., BeO, AIN, . . . ) do not haveto be carefully joined and a gap can be left between one piece and thenext. The gap can vary in size (e.g., one to three mm or more).Moreover, the top and bottom electrode can be shaped independently ofthe ceramic and each other, to form a profile that provides a betterbeam mode profile. For example some or all of the four corners of thewaveguide can be rounded to suppress higher order mode formations, andthe distance between the top and bottom electrodes can be decreasedalong the ceramic sidewalls to allow for easier gas discharge initiationwhile maintaining the same overall gap size and consequently havingapproximately the same discharge volume (i.e. gain volume).

In exemplary embodiments of the present invention the various shapes ofthe electrodes allows higher peak power compared to related art devices.FIGS. 9A-C illustrate various electrode protrusion shapes in accordancewith exemplary embodiments of the present invention. The protrusions(also referred to as nips) result in stronger electric fields in alimited regional area, thereby aiding in the startup of the laser. Suchprotrusions allow startups at pressures higher than conventional lasers.The increased laser pressure results in an increase of gain volume andsubsequent increase pulse power capabilities, but with a decrease in theaverage power emitted from the laser. An exemplary embodiment of thepresent invention increases the temporal pulse length to maintain totalpulsing power. Thus, quicker start and stop times can be achieved, withincreased efficiency, while maintaining total emitted power, whencompared to related art devices.

FIG. 10 illustrates the connection of at least one power source inaccordance with an exemplary embodiment of the present invention. Apower source 30 is connected to a connector 12, which feeds power fromthe power source through the housing 11. In an exemplary embodiment ofthe present invention the power source is an radio frequency (RF). powersource. A RF power supply for any gas laser is composed of one or moreRF power transistors and control circuitry for both the transistor(s)and the interface between the RF power supply and the laser. The RFfrequency that the transistors generate is unique to every laser buttypically is at 40.68, 81.36 or 100 MHz. The control circuitry for theRF power transistors regulates both the RF oscillation and the RF poweron/off switching. Conventional RF power systems use relatively olddesign practices in the transistor drive circuitry, because the RF powertransistor's oscillations at 40 to 100 MHz disrupt any microprocessor'scircuitry. Consequently the RF power transistor circuitry is presentlydesigned to incorporate discreet components that are virtuallyinsensitive to the power transistor's oscillations.

In an exemplary embodiment of the present invention, the RF power supplycan be microprocessor 32 controlled. In this embodiment themicroprocessor 32 runs at a frequency higher than the 40 to 100 MHzlevel of the RF power transistors. For example a processor at ten timesthe RF power level would be at 100 MHz×10=1.0 GHz. Any signal ‘pickedup’ by the GHz processor can be significantly below its noise thresholdsuch that the processor's operation is not impaired. Consequently themicroprocessor 32 can replace existing discreet component circuitry thatcontrols the RF power transistors. For example, various parts of thediscrete 'ITL logic circuitry can be replaced by the microprocessor 32,for example a one shot discrete IC, that is part of the RF powertransistor's VSWR protection circuit, can be eliminated. Additionally,various orgates, opamps and comparators can be eliminated. Otherportions of the power system can be replaced by the microprocessor 32and the discussion herein should not be interpreted to limit theportions replaced.

The use of a microprocessor 32 allows the RF power supply board to bemanufactured at a lower cost and for the supply to be significantlysmaller. The elimination of numerous discreet components greatlyincreases the microprocessor based supply's reliability compared toexisting designs. The discussion herein is not intended to limit thenumber or type of microprocessor that can be used with/in the RF powersupply.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the embodiments of the presentinvention. Such variations are not to be regarded as a departure fromthe spirit and scope of the present invention (e.g., other gases besidesCO2 or CO2 mixtures can be used; protrusions can be used with an allmetal system, where the ceramic side walls are replaced with metallicside walls; additional waveguides can be used as coolant chambers, . . .).

1-37. (canceled)
 38. A laser comprising: first and second electrodes, alaser waveguide defined between at least first and second electrodes,and at least one protrusion on the first and/or second electrode, theprotrusion extending into the waveguide of the laser from the firstand/or second electrode.
 39. The laser of claim 38, wherein protrusionsare formed on each of the first and second electrodes, and wherein thelaser is a waveguide laser.
 40. The laser of claim 38, where the atleast one protrusion aids in starting characteristics of the laser byincreasing the electric field in localized region(s) of the cavity. 41.The laser of claim 38, wherein the waveguide laser is a CO₂ laser thatuses a gaseous lasing material comprising CO₂.
 42. The laser of claim38, wherein an electromagnetic field is caused by an oscillating currentsupplied to at least one of the electrodes such that the electromagneticfield is provided in a cavity of the waveguide.